利用新型激光场探测和调控分子超快动力学

With the fast development of novel laser techniques, the atomic-scale resolution of the electron motion in matter can been achieved. Different from atoms, the molecule has more degrees of freedom and shows more complex effects in strong laser fields. To probe and control the electron motion within molecules is more difficult than atoms. In this project, we will explore the procedure of probing the ultrafast dynasics of the molecule with novel laser techniques. First, we will study the influence of the molecular orientation and the molecular structure on ionization and high-order harmonic generation (HHG) as the molecule is exposed to a strong orthogonally-polarized two-colour laser field. We will focus on the roles of the time delay between these two fields, charge-resonance effects, interference effects and the permanent dipole in ionization and HHG of symmetric and asymmetric molecules. With these studies, we will further explore the procedure of probing and cotrolling the ultrafast electron dynamics of molecules using orthogonally-polarized two-colour laser fields. Secondly, we will investigate the ionization from molecules as exposed to strong elliptically-polarized laser fields.We will study the roles of the molecular orientation, the excited states, the permanent dipole and two-center interference in ionization and explore the relation between the the molecular ionization and the ellipticity of the field, aiming at the possible procedures of probing and controlling the ultrafast electron dynamics of molecules with elliptically polarized laser fields. These studies are expected to give suggestions on relevant studies in experiments.

新型激光场的应用，使人们有可能在阿秒时间尺度观测物质中电子的超快运动。相比于原子，分子由于具有更多的自由度，在强激光场中呈现了许多新的效应，对其超快电子动力学的探测和操控更加困难。本项目将从理论上详细研究利用新型激光场探测分子内部电子超快动力学的方案，主要内容是：1）研究正交极化双色激光场中分子电离和谐波辐射与分子结构、取向以及双色光之间的时间延迟的关系，研究对称分子的电荷共振效应、干涉效应和不对称分子的固有偶极子效应对该关系的影响，进而探索利用正交极化双色场探测和调控极性和非极性分子超快电子动力学的方案；2）研究椭圆极化激光场中分子电离与分子结构、取向以及激光场椭偏率之间的关系，研究电荷共振、固有偶极子效应和激发态效应对该关系的影响，进而探索利用椭圆极化激光场探测和调控分子超快电子动力学的方案。本项目的研究将为相关的实验研究提供一定的理论支持。

围绕新型光场调控物理及应用，聚焦分子超快动力学的探测和调控问题，通过发展包含核振动的数值模拟方案和包含库伦效应的强场近似模型，研究了正交极化双色场和椭圆极化激光场中对称和不对称分子（极性分子）的阈上电离和高次谐波辐射，分析了取向效应、固有偶极子效应和库伦效应等对分子电离和谐波辐射的重要影响。特别是：1）从半经典的角度，提出了库伦导致的电离时间延迟概念，将库伦效应对强场电离和谐波辐射的复杂影响简化为对电子轨道在时域上的修正，利用这一概念解释了单电离、双电离和谐波辐射中的系列现象；因为电子轨道是通过实验观测量反演系统阿秒尺度时域信息的基本理论工具，这一概念对相关实验研究预期将有积极的推动作用。2）建立了包含库伦效应和固有偶极子效应的不对称分子电离和谐波辐射的理论模型，解释了极性分子光电子动量分布最显著的特征——左右不对称性的物理起源，解决了极性分子强场动力学研究中长期缺乏适合的基本理论模型的问题，相信将对极性分子超快探测研究起到积极的促进作用。